PALEOECOLOGY OF THE MIDDLE CAMBRIAN EOCRINOID ECHINODERM GOGIA SPIRALIS: POSSIBLE CHANGES IN SUBSTRATE ADAPTATIONS THROUGH ONTOGENY

Late Proterozoic seafloor sediment had well-developed microbial mats and poorly developed vertically oriented bioturbation. This condition changed gradually and episodically during the Cambrian as a result of burrowing organisms with an increasing vertical orientation to their bioturbation. The goal of this research is to increase our understanding of the paleoecology of the middle Cambrian eocrinoid echinoderm Gogia spiralis in the context of this substrate transition, focusing on its substrate adaptations through ontogeny and a characterization of the seafloor on which it lived. G. spiralis is preserved in the middle Cambrian Wheeler Shale, House Range, Utah and was likely a dysaerobic zone inhabitant (Gaines 2003). It is found in two general forms: one with a small basal attachment pad, and the other with a pointed or blunt basal end that lacks an attachment pad (Robison, 1965). The hypothesis being tested in this study is that these two forms represent a juvenile-to-adult shift in substrate adaptations, with G. spiralis developing from a sediment attacher as a juvenile to a shallow sediment sticker as an adult. Multiple specimens were collected during this research and these, along with specimens housed at the University of Utah Natural History Museum, will be examined in detail. Thecal height, which is a useful proxy for developmental stage, will be measured and substrate adaptation (attachment pad vs. blunt basal end) will be recorded for each specimen. If specimens with small thecal heights typically have attachment pads while those with large thecal heights typically have blunt basal ends, then the hypothesis outlined above will be supported. Outcrops at eight localities within the Wheeler Shale where G. spiralis has been found preserved were also sampled in order to examine bioturbation levels. Utilizing x-radiography, these samples will be inspected for bioturbation levels, using the ichnofabric index (ii) method. Low bioturbation levels will indicate that G. spiralis lived on firm, Proterozoic-style substrates. G. spiralis may therefore provide an example of a benthic metazoan adapted to firm Proterozoic-style substrates in different ways during its ontogeny, exemplifying the profound impact that the destruction of such substrates in normal marine settings would have had on the Cambrian benthos.